Thanks charron,but it's actually the 700/701 model we have on board, not the 440 (my mistake ) . It's fitted on 4 of our 76s, it was working well when new, but now we reguraly have to change the Receiver / Transmitter.
We reach the point were we find ourselves AOG, because spares are so long to reach us (our MLE forbids offshore fllight with inop weather radar)
There is no particular error message and the test pattern is correct.
Symptoms are usually nothing shown on the screen even with obviously reportable weather. Sometimes, it works well for about 10 mins time with good returns and then,suddenly nothing. (A bit as if a component was overheating...)